Novel two-particle electrophoretic ink for microencapsulated flexible electronic display

ABSTRACT

Exemplary electrophoretic ink capsules for electrophoretic displays, and methods for making the exemplary electrophoretic ink capsules are disclosed. In various embodiments, the electrophoretic ink capsules can include triboelectrically charged electrophoretic particles having higher electrical conductivity than conventionally charged electrophoretic particles allowing fabrication of electrophoretic displays with lower switching fields and faster response times.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 11/165,231,filed Jun. 24, 2005, entitled “Novel Two-Particle Electrophoretic Inkfor Microencapsulated Flexible Electronic Display”, which is herebyincorporated by reference in its entirety.

DESCRIPTION OF THE INVENTION

1. Field of the Invention

The present teachings relate to electrophoretic displays and, moreparticularly, relates to eletrophoretic ink and methods for makingelectrophoretic ink for encapsulated electrophoretic displays.

2. Background of the Invention

An electrophoretic display is a flexible display having many attributesof a paper document. For example, it can look like paper, have ambientlight valve behavior like paper (i.e. the brighter the ambient light,the more easily it may be seen), be flexible like paper, be carriedaround like paper, be written on like paper, be copied like paper, andhave nearly the archival memory of paper.

Encapsulated electrophoretic displays typically consist of a polymericbinder surrounding ink capsules. The ink capsules or “electrophoreticink” have electrophoretic particles and a liquid within. The particlesare of two types, one type that substantially reflects light and anothertype that absorbs light. A pair of electrodes is located adjacent thebinder to apply an electric field. Application of one electric fieldcauses the particles to orient so that the capsules reflect light.Application of another electric field causes the particles to orient sothat the capsules absorb light.

In order to respond to the electric field, the electrophoretic particlesare charged. Problems arise, however, because conventionalelectrophoretic ink requires a complex mixture of ionic charge additivesand ionic charge control agents in addition to the pigments,dispersants, and solvents. Moreover, the presence of those ionicadditives results in a highly charged electrophoretic ink that requiresa high switching field to move the particles within the capsules.

Thus, there is a need to overcome these and other problems of the priorart to provide an electrophoretic ink that can be used in anelectrophoretic display having a low switching field and a fast responsetime.

SUMMARY OF THE INVENTION

According to various embodiments, the present teachings include anelectrophoretic ink capsule including a first plurality oftriboelectrically charged particles, a second plurality oftriboelectrically particles, and a non-polar liquid. The electrophoreticink capsule can further include a shell encapsulating the firstplurality of particles, the second plurality of particles, and thenon-polar liquid, wherein the first plurality of triboelectricallycharged particles move in a first direction within the non-polar liquidin response to an applied electric field and the second plurality oftriboelectrically charged particles move in an opposite direction withinthe non-polar liquid in response to the applied electric field.

According to various other embodiments, the present teachings include amethod for making electrophoretic ink capsules including forming a firstplurality of charged particles having a first pigment by feeding a firstpigmented polymer melt onto a spinning disk. A second plurality ofcharged particles having a second pigment can be formed by feeding asecond pigmented polymer melt onto the spinning disk. A first pluralityof fine particles can be formed by mechanically breaking up the firstplurality of charged particle. A second plurality of fine particles canalso be formed by mechanically breaking up the second plurality ofcharged particles. A plurality of electrophoretic ink capsules can beformed by encapsulating a portion of the first plurality of chargedparticles, a portion of the second plurality of charged particles, and anon-polar liquid.

In still further embodiments, the present teachings include anelectrophoretic display including a first substrate and a conductivelayer on the first substrate. The electrophoretic display can furtherinclude a first polyvinyl acetate layer comprising a plurality ofelectrophoretic ink capsules having an electrical conductivity of about10⁻¹¹ Scm⁻¹ or less. The electrophoretic ink capsules can comprise ashell encapsulating a plurality of triboelectrically charged darkparticles, a plurality of triboelectrically charged light particles, anda non-polar liquid.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention, as claimed.

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate several embodiments of theinvention and together with the description, serve to explain theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an exemplary eletrophoretic ink particle in accordancewith the present teachings.

FIG. 2 depicts an exemplary monochrome spinner used to make exemplaryeletrophoretic ink particle in accordance with the present teachings.

FIGS. 3A and 3B depict the movement of exemplary eletrophoretic inkparticles in response to an electric field.

FIG. 4 depicts an exemplary electrophoretic display including exemplaryeletrophoretic ink particle in accordance with the present teachings.

DESCRIPTION OF THE EMBODIMENTS

In the following description, reference is made to the accompanyingdrawings that form a part thereof, and in which is shown by way ofillustration specific exemplary embodiments in which the invention maybe practiced. These embodiments are described in sufficient detail toenable those skilled in the art to practice the invention and it is tobe understood that other embodiments may be utilized and that changesmay be made without departing from the scope of the invention. Thefollowing description is, therefore, not to be taken in a limited sense.

FIGS. 1-4 depict exemplary electrophoretic ink capsules forelectrophoretic displays, and methods for making the exemplaryelectrophoretic ink capsules. In various embodiments, theelectrophoretic ink capsules can include triboelectrically chargedelectrophoretic particles having higher electrical conductivity thanconventionally charged electrophoretic particles allowing fabrication ofelectrophoretic displays with lower switching fields and faster responsetimes.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements. Moreover, all ranges disclosed hereinare to be understood to encompass any and all sub-ranges subsumedtherein. For example, a range of “less than 10,” can include any and allsub-ranges between (and including) the minimum value of zero and themaximum value of 10, that is, any and all sub-ranges having a minimumvalue of equal to or greater than zero and a maximum value of equal toor less than 10, e.g., 1 to 5.

As used herein, the term “triboelectrically charged particles” refers toparticles having a charge, either positive or negative, created by theircontact and separation with another material.

According to various embodiments, an exemplary electrophoretic inkcapsule 105 is shown in FIG. 1. Electrophoretic ink capsule 105 caninclude a shell 110, a non-polar liquid 120, a first plurality oftriboelectrically charged particles 130 and a second plurality oftriboelectrically charged particles 140. In various embodiments,electrophoretic ink capsule 105 can have an electrical conductivity ofabout 10⁻¹¹ Scm⁻¹ or less. Electrophoretic ink capsule 105 can furtherhave a diameter of about 200 μm or less.

Shell 110 can encapsulate non-polar liquid 120, first plurality ofparticles 130, and second plurality of particles 140. Shell 110 can bespherical or non-spherical in shape. According to various embodiments,shell 100 can formed by, for example, interfacial polymerization, insitu polymerization, physical processes, such as coextrusion and otherphase separation processes, in-liquid curing, and simple/complexcoacervation.

Exemplary materials for shell 110 formed by a simple coacervationprocesses include, but are not limited to, gelatin, polyvinyl alcohol,polyvinyl acetate, and cellulosic derivatives, such as, for example,carboxymethylcellulose. Exemplary materials for shell 110 formed by acomplex coacervation processes include, but are not limited to, gelatin,acacia, carageenan, carboxymethylcellulose, hydrolyzed styrene anhydridecopolymers, agar, alginate, casein, albumin, methyl vinyl etherco-maleic anhydride, and cellulose phthalate. Exemplary materials forshell 110 formed by a phase separation processes include, but are notlimited to, polystyrene, PMMA, polyethyl methacrylate, polybutylmethacrylate, ethyl cellulose, polyvinyl pyridine, and polyacrylonitrile. Exemplary materials for shell 110 formed by an in situpolymerization processes include, but are not limited to,polyhydroxyamides, with aldehydes, melamine, or urea and formaldehyde;water-soluble oligomers of the condensate of melamine, or urea andformaldehyde; and vinyl monomers, such as, for example, styrene, MMA,and acrylonitrile. Exemplary materials for shell 110 formed by aninterfacial polymerization processes include, but are not limited to,diacyl chlorides, such as, for example, sebacoyl, adipoyl, and di- orpoly-amines or alcohols, and isocyanates. Useful emulsion polymerizationmaterials include, but are not limited to, styrene, vinyl acetate,acrylic acid, butyl acrylate, t-butyl acrylate, methyl methacrylate, andbutyl methacrylate.

Non-polar liquid 120 can be selected, for example, based on propertiessuch as density, refractive index, and solubility, and/or based onchemical inertness, density matching to plurality of electrophoreticparticles 130 and 140, and/or chemical compatibility with bothelectrophoretic particles 130 and 140 and shell 110. According tovarious embodiments, non-polar liquid 120 can comprise a single fluid ora blend of more than one fluid.

According to various embodiments non-polar liquid 120 can be, forexample, an organic liquid, such as halogenated organic liquid, asaturated linear or branched hydrocarbon, a silicone polymeric liquid.Examples of a hydrocarbon non-polar liquid 120 include, but are notlimited to, dodecane, tetradecane, the aliphatic hydrocarbons in theIsopar ® series (Exxon, Houston, Tex.), Norpar.®. (series of normalparaffinic oils), Shell-Sol.®. (Shell, Houston, Tex.), and Sol-Tro I®.(Shell, Houston, Tex.), naphtha, and other petroleum liquids. Examplesof halogenated liquids are, but are not limited to, Halocarbon 0.8 and1.8 from Halocarbon Inc. Examples of silicone polymeric liquids include,but are not limited to, DC200 from Dow Corning Inc.

First plurality of triboelectrically charged particles 130 and a secondplurality of triboelectrically charged particles 140 can include apigment and a polymer. According to various embodiments, the firstplurality of triboelectrically charged particles 130 can be dark coloredparticles, such as, for example, light absorbing particles. Secondplurality of charged particles 140 can be light colored particles, suchas, for example, light reflecting particles.

Pigments can include, but are not limited to, PbCrO₄, Cyan blue GT55-3295 (American Cyanamid Company, Wayne, N.J.), Cibacron Black BG(Ciba Company, Inc., Newport, Del.), Cibacron Turquoise Blue G (Ciba),Cibalon Black BGL (Ciba), Orasol Black BRG (Ciba), Orasol Black RBL(Ciba), Acetamine Blac, CBS (E. I. du Pont de Nemours and Company, Inc.,Wilmington, Del.), Crocein Scarlet N Ex (du Pont) (27290), Fiber BlackVF (duPont) (30235), Luxol Fast Black L (duPont) (Solv. Black 17),Nirosine Base No. 424 (duPont) (50415 B), Oil Black BG (duPont) (Solv.Black 16), Rotalin Black RM (duPont), Sevron Brilliant Red 3 B (duPont);Basic Black DSC (Dye Specialties, Inc.), Hectolene Black (DyeSpecialties, Inc.), Azosol Brilliant Blue B (GAF, Dyestuff and ChemicalDivision, Wayne, N.J.) (Solv. Blue 9), Azosol Brilliant Green BA (GAF)(Solv. Green 2), Azosol Fast Brilliant Red B (GAF), Azosol Fast OrangeRA Conc. (GAF) (Solv. Orange 20), Azosol Fast Yellow GRA Conc. (GAF)(13900 A), Basic Black KMPA (GAF), Benzofix Black CW-CF (GAF) (35435),Cellitazol BNFV Ex Soluble CF (GAF) (Disp. Black 9), Celliton Fast BlueAF Ex Conc (GAF) (Disp. Blue 9), Cyper Black IA (GAF) (Basic Blk. 3),Diamine Black CAP Ex Conc (GAF) (30235), Diamond Black EAN Hi Con. CF(GAF) (15710), Diamond Black PBBA Ex (GAF) (16505); Direct Deep Black EAEx CF (GAF) (30235), Hansa Yellow G (GAF) (11680); Indanthrene Black BBKPowd. (GAF) (59850), Indocarbon CLGS Conc. CF (GAF) (53295), KatigenDeep Black NND Hi Conc. CF (GAF) (15711), Rapidogen Black 3 G (GAF)(Azoic Blk. 4); Sulphone Cyanine Black BA-CF (GAF) (26370), ZambeziBlack VD Ex Conc. (GAF) (30015); Rubanox Red CP-1495 (TheSherwin-Williams Company, Cleveland, Ohio) (15630); Raven 11 (ColumbianCarbon Company, Atlanta, Ga.), (carbon black aggregates with a particlesize of about 25 μm), Statex B-12 (Columbian Carbon Co.) (a furnaceblack of 33 μm average particle size), and chrome green.

Polymers for first plurality of triboelectrically charged particles 130and second plurality of triboelectrically charged particles 140 caninclude polymers having a melting temperature of about 70° C. to about300° C. Polymers include, but are not limited to, polyethylene andpolypropylene. Referring to FIGS. 3A and 3B, a pair of electrodes 325and 345 can be positioned adjacent a binder layer 315 to apply anelectric field. Application of one electric field causes first pluralityof triboelectrically charged particles 140 to move such that capsule 105appears dark, e.g., to absorb light, to an observer 301. Application ofanother electric field causes second plurality of triboelectricallycharged particles 130 to move such that capsule 105 appears light, e.g.to reflect light, to observer 301.

Referring to FIG. 2, triboelectrically charged particles can be formed,for example, using a monochrome spinner 260. According to variousembodiments, triboelectrically charged spheres having a diameter ofabout 75 μm and less can be formed by forming a polymer melt including apigment and a polymer. In various embodiments, a non-ionic surfactantcan be included. The polymer melt can be housed in a reservoir 270 ofmonochrome spinner 260. The polymer melt, heated by a shroud heater 290,can be fed from a nozzle 280 to a spinning disk 295. Spinning disk 295can have a spinning speed of about 1,000 rpm to about 10,000 rpm.Spinning disk 295 can triboelectrically charge and eject sphericalparticles 230. The resultant charged (either positively or negatively)spheres 230 can then be mixed with a liquid and metal shot, and shakento form fine triboelectrically charged particles having a diameter of 15μm and less. One of ordinary skill in the art understands that whetherthe particles become positively or negatively charged depends on therelative tendencies of the particle material and the spinning diskmaterial to gain or lose electrons.

An exemplary electrophoretic ink capsule and an exemplary method formaking the electrophoretic ink capsule will be described. It is to beunderstood that the disclosed examples are exemplary and in no way areintended to limit the scope of the invention.

EXAMPLE

According to various embodiments, an electrophoretic ink capsule caninclude a first plurality of triboelectrically charged particles thatcan absorb light, such as, for example, dark and/or black particles, anda second plurality of triboelectrically charged particles that canreflect light, such as, for example, light and/or white particles. Theblack particles comprised, for example, an extruded black pigmented waxincluding 20 wt % Ferro 6331 black pigment (Ferro Corp., Cleveland,Ohio)+0.3 wt % Igepal DM970 (Aldrich, St. Louis, Mo.)+79.7% Polywax 2000(Baker Petrolite, Sugar Land, Tex.). The black pigmented wax was meltedat about 150° C. and mechanically stirred for two hours at about1200-1500 rpm. The wax melt was then fed into a monochrome spinner witha disk spinning at about 5930 rpm, a shroud temperature of about 170°C., and a nozzle temperature of about 125° C. The resultant blackspheres were about 75 μm in diameter. Furthermore, the black sphereswere positively charged by tribocharging.

Approximately 5 grams of the black spheres were then mixed with 15 gramsof Isopar M and 20 grams of stainless steel shot, about 5 mm indiameter, in a 30 ml polyproplyene bottle. The bottle was shaken in apaint shaker for approximately 90-120 minutes. The resultanttriboelectrically charged black particles were about 15 μm in diameter.

The white particles comprised, for example, an extruded white pigmentedwax including 30 wt % Dupont R104 TiO₂ pigment+70 wt % Polywax 2000. Thewhite pigmented wax was melted at about 150° C. and mechanically stirredfor two hours at about 1200-1500 rpm. The wax melt was then fed into amonochrome spinner with a disk spinning at about 5930 rpm, a shroudtemperature of about 170° C., and a nozzle temperature of about 125° C.The resultant white spheres were about 75 μm in diameter and negativelycharged by tribocharging.

Approximately 5 grams of the white spheres were then mixed with 15 gramsof Isopar M and 20 grams of zirconia shot, about 5 mm in diameter, in a30 ml polyproplyene bottle. The bottle was shaken in a paint shaker forapproximately 90-120 minutes. The resultant triboelectrically chargedwhite particles were about 15 μm in diameter.

The triboelectrically charged black and white particles were thenencapsulated using a complex coacervation process under high shearprovided by an overhead mixer with a 3-blade impeller. A 40 mL particlemixture of triboelectrically charged black and white particles in IsoparM was prepared, the triboelectrically charged black and white particlescomprising about 21 wt % of the mixture. The ratio of black particles towhite particles was about 1.5:1. An encapsulation solution was alsoprepared by mixing 100 mL of a 6.6% gelatin solution, 400 mL of water,and 100 mL of a 6.6 gum Arabic solution. The pH of the encapsulationsolution was adjusted to about 4.5 by addition of a dilute acetic acidsolution. The encapsulation solution was then heated to about 40° C. Theparticle mixture was added to the encapsulation mixture and allowed tocool to room temperature. The resultant capsules were crosslinked withgluteraldenhyde, washed with water, and wet-sieved to isolate capsulesapproximately 200 μm or less.

Referring to FIG. 4, an exemplary electrophoretic display 400 is shown.According to various embodiments, electrophoretic display 400 caninclude a plurality of electrophoretic ink capsules 405 embedded in aPVA layer 415. Electrophoretic ink capsules 405 can include a shellencapsulating a plurality of triboelectrically charged dark particles,such as, for examples black particles, a plurality of triboelectricallycharged light particles, such as., for example, white particles, and anon-polar liquid. Although depicted as a single layer, PVA layer 415 cancomprise several layers of PVA. PVA layer 415 can be disposed on a firstconductive indium-tin-oxide (ITO) layer 425. First conductive ITO layer425 can be disposed on a first substrate 435, such as, for example, aMylar substrate. Electrophoretic display 400 can further include asecond conductive ITO layer 445 disposed on a second substrate 455, suchas, for example, a Mylar substrate. Second conductive ITO layer 445 canbe bonded to PVA layer 415 by, for example, a layer of glue 465.According to various embodiments, electrophoretic display 400 can have aswitching field of about 2 Volts/μm and a switching speed of 15 to 20Hertz.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

1. A method for making electrophoretic ink capsules comprising: forminga first plurality of charged particles having a first pigment by feedinga first pigmented polymer melt onto a spinning disk; forming a secondplurality of charged particles having a second pigment by feeding asecond pigmented polymer melt onto the spinning disk, forming a firstplurality of fine particles by mechanically breaking up the firstplurality of charged particles; forming a second plurality of fineparticles by mechanically breaking up the second plurality of chargedparticles; forming a plurality of electrophoretic ink capsules byencapsulating a portion of the first plurality of charged particles, aportion of the second plurality of charged particles, and a non-polarliquid.
 2. The method of claim 1, wherein the step of forming a firstplurality of charged particles comprises: forming the first pigmentedpolymer melt by melting a black pigmented polyethylene; stirring thefirst pigmented polymer melt; and feeding the first pigmented polymermelt into a monochrome spinner, wherein a shroud temperature of themonochrome spinner is about 80° C. to 300° C., a nozzle temperature ofthe monochrome spinner is about 90° C. to 170° C., and a disk speed ofthe monochrome spinner is about 1,000 rpm to 10,000 rpm.
 3. The methodof claim 1, wherein the step of forming a first plurality of chargedparticles comprises: forming the second pigmented polymer melt bymelting a white pigmented polyethylene wax; stirring the secondpigmented polymer melt; and feeding the second pigmented polymer meltinto a monochrome spinner, wherein a shroud temperature of themonochrome spinner is about 80° C. to 300° C., a nozzle temperature ofthe monochrome spinner is about 90° C. to 170° C., and a disk speed ofthe monochrome spinner is about 1,000 rpm to 10,000 rpm.
 4. The methodof claim 1, wherein the step of forming a first plurality of fineparticles comprises: forming a mixture comprising the first plurality offine particles with the non-polar liquid, and a plurality of stainlesssteel shot having a diameter of about 5 mm or less; and shaking themixture for about 90 minutes or more.
 5. The method of claim 1, whereinthe step of forming a second plurality of fine particles comprises:forming a mixture comprising the second plurality of fine particles withthe non-polar liquid, and a plurality of zirconia shot having a diameterof about 5 mm or less; and shaking the mixture for about 90 minutes ormore.
 6. The method of claim 1, wherein the step of forming a pluralityof electrophoretic ink capsules comprises: forming a mixture comprisingthe first plurality of fine particles, the second plurality of fineparticles, and the non-polar liquid, wherein the ratio of the firstplurality of fine particles to the second plurality of fine particles isabout 1.5 to 1 or less; preparing an encapsulation solution comprising agelatin solution, water, and a gum Arabic solution, adjusting the pH ofthe encapsulation solution to about 4.5; pouring the mixture into theencapsulation solution, cooling the mixture to about room temperature toform a plurality of capsules comprising a gum Arabic gelatin shell; andcross linking the shell of the plurality of capsules.
 7. The method ofclaim 6, wherein the step of adjusting the pH of the encapsulationsolution comprises addition of a dilute acetic acid solution.
 8. Themethod of claim 7, further comprising washing the plurality of capsuleswith water and isolating a desired capsule size.